The Hitch Hikers film is a great film, but purists have criticised it because it hardly holds true to the original material. If you want to see for yourself BBC2 starts showing the original TV series tonight at 11:20. I seen the TV series a few years ago and although it is very dated, the material shines through and it is a series you won't easily forget.
EDIT: Incidentally directly afterwords is Barbarella, one of the strangest Sci-fi films ever made. I mean its hard to sell wither its a parody of Scifi, or a parody of porn.
And then at 1:45 on Channel4 is Don't be a Menace to South Central While Drinking Your Juice in The Hood. Which takes the mickey of Black stereotypes, and isn't a film for the easily offended, but it is funny.